Johnson thermo-electrochemical converter

Abstract

A electrochemical direct heat to electricity converter having a low temperature membrane electrode assembly array and a high temperature membrane electrode assembly array is provided. Additional cells are provided in the low temperature membrane electrode assembly array, which causes an additional amount of the working fluid, namely hydrogen, to be pumped to the high pressure side of the converter. The additional pumped hydrogen compensates for the molecular hydrogen diffusion that occurs through the membranes of the membrane electrode assembly arrays. The MEA cells may be actuated independently by a controller to compensate for hydrogen diffusion.

I claim: 
     
       1. An electrochemical direct heat to electricity converter comprising:
 a working fluid; 
 a first membrane electrode assembly coupled to a heat sink and a second membrane electrode assembly coupled to a heat source, each of the first and second membrane electrode assemblies including a first porous electrode and a second porous electrode and at least one ion conductive membrane sandwiched between the first and second porous electrodes, the first membrane electrode assembly operating at a temperature of the heat sink and producing a voltage based on the temperature of the heat sink, and the second membrane electrode assembly operating at a temperature of the heat source and producing a voltage based on the temperature of the heat source; 
 an external load connected in series with the first and second membrane electrode assemblies, a difference in voltage between the first and second membrane electrode assemblies being applied to the external load, current flow through both the first and second membrane electrode assemblies being the same; 
 at least one first conduit containing the working fluid at a first pressure and at least one second conduit containing the working fluid at a second pressure which is higher than the first pressure, the at least one first conduit being coupled to the first porous electrodes to form a low pressure side of the converter, the at least one second conduit being coupled to the second porous electrodes to form a high pressure side of the converter, the working fluid circulating continuously between the first and second membrane electrode assemblies, the working fluid being expanded in one of the first and second membrane electrode assemblies from the high pressure side to the low pressure side and being compressed in the other one of the first and second membrane electrode assemblies from the low pressure side to the high pressure side under the same current flow, such that a constant pressure differential is maintained; and 
 a controller configured to (i) monitor a pressure of the first membrane electrode assembly and a pressure of the second membrane electrode assembly, (ii) determine an extent of loss of pressure differential resulting from molecular diffusion of the working fluid through the ion conductive membranes of the first or second membrane electrode assembly, and (iii) actuate at least one of the first membrane electrode assembly and the second membrane electrode assembly to pump an additional amount of the working fluid from the low pressure side to the high pressure side when the pressure differential drops below a predetermined value in order to maintain the pressure across the ion conductive membranes. 
 
     
     
       2. The electrochemical direct heat to electricity converter according to  claim 1 , further comprising heat exchanger means for transferring heat from the at least one second conduit to the at least one first conduit. 
     
     
       3. The electrochemical direct heat to electricity converter according to  claim 1 , wherein the converter comprises a plurality of first membrane electrode assemblies electrically connected in series with each other. 
     
     
       4. The electrochemical direct heat to electricity converter according to  claim 1 , wherein the working fluid is selected from a group consisting of oxygen, hydrogen and sodium. 
     
     
       5. The electrochemical direct heat to electricity converter according to  claim 4 , wherein the working fluid is hydrogen. 
     
     
       6. The electrochemical direct heat to electricity converter according to  claim 4 , wherein the converter comprises a plurality of second membrane electrode assemblies, and wherein a number of the plurality of first membrane electrode assemblies is greater than a number of the plurality of second membrane electrode assemblies, and wherein the greater number of the plurality of first membrane electrode assemblies causes an additional amount of the working fluid to be pumped from the low pressure side to the high pressure side of the converter, in order to compensate for the loss of pressure differential resulting from molecular diffusion of the working fluid through the ion conductive membranes. 
     
     
       7. The electrochemical direct heat to electricity converter according to  claim 1 , wherein the controller is configured to monitor a temperature of the first membrane electrode assembly and a temperature of the second membrane electrode assembly.